Surface acoustic wave device

ABSTRACT

A surface acoustic wave device includes a sealing resin for sealing a gap between a surface acoustic wave element and a mounting board. The sealing resin is prevented from flowing so as to reach a vibrating portion of the surface acoustic wave element. In the surface acoustic wave device, a surface acoustic wave element is connected to a mounting board through bumps, the outer peripheral edge of the surface acoustic wave element is sealed by a sealing resin, and a vibration space is secured between the vibrating portion of the surface acoustic wave element and mounting board. In the surface acoustic wave element, an outer barrier enclosing the bumps and the vibrating portion and an inner barrier enclosing the vibrating portion are provided, the height of the outer barrier is lower than the total height of the height of the bumps and the height of electrode lands formed on the mounting board, and the height of the inner barrier is lower than the height of the bumps.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a surface acoustic wave deviceand more particularly, to a surface acoustic wave device in which asealing resin for sealing a gap between a surface acoustic wave elementand a mounting board is prevented from flowing so as to reach avibrating portion of the surface acoustic wave element.

[0003] 2. Description of Related Art

[0004] One example of a known surface acoustic wave device is disclosedin Patent Document 1 (Japanese Unexamined Patent Application PublicationNo. 8-316778) and its structure is shown in FIG. 21. In this the surfaceacoustic wave device 51, a surface acoustic wave element (SAW devicechip) 52 and a mounting board 53 are integrated and the functionalsurface of the surface acoustic wave element 52 is connected to themounting board 53 through bumps 54.

[0005] On the functional surface of the surface acoustic wave element52, as shown in FIG. 22, a vibrating portion 56 including a comb-shapedelectrode portion (hereinafter called an IDT), etc., is provided, avibration space 7 is secured between the vibrating portion 56 and themounting board 53, and the outer peripheral edge of the surface acousticwave element 52 is sealed by using a sealing resin 58 composed of athermosetting resin such as an epoxy resin, etc. Moreover, on themounting surface of the mounting board 53, as shown in FIG. 23,electrode lands 59 for connecting the bumps 54 at fixed locations areformed.

[0006] Furthermore, in the surface acoustic wave device 51, in order toprevent the sealing resin 58 for sealing a gap between the surfaceacoustic wave element 52 and the mounting board 53 from flowing to thevibrating portion 56 of the surface acoustic wave element 52, two innerand outer barriers 61 and 62 that block the resin flow, which are madelower than the bumps 54 and disposed so as to enclose the vibratingportion 56, are provided on the functional surface of the surfaceacoustic wave element 52. That is, the barriers 61 and 62 are formed byusing a photoresist and function as a barrier for preventing the sealingresin 56 from flowing in. The reason why these barriers 61 and 62 areset lower than the bumps 51 is that, when the surface acoustic waveelement 52 is flip-chip bonded to the mounting board 53, even if thebumps 54 are pressed, the bumps 54 have a sufficient connecting strengthand a small gap is secured between the barriers 61 and 62 and themounting board 53.

[0007] In the surface acoustic wave device 51 constructed in this way,the sealing resin 58 coated for sealing the outer peripheral edge of thesurface acoustic wave element 52 reaches a gap between the outer barrier61 and the mounting board 53 due to the surface tension and, accordingto circumstances, reaches a gap between the inner barrier 62 and themounting board 53. However, since the gap is narrow, the sealing resin58 does not flow in over the barriers 61 and 62 and, as a result, thesealing resin 58 is prevented from flowing in so as to reach thevibrating portion 56 of the surface acoustic wave element 52.

[0008] However, in the related surface acoustic wave device 51 describedabove, the relative location of the barriers 61 and 62 and the bumps 54is not considered and the two barriers 61 and 62 are provided only toenclose the vibrating portion 56. Then, each of the barriers 61 and 62faces the electrode lands 59 or faces the mounting surface of themounting board 53 which is exposed, without having the electrode lands59 formed therebetween. In such a case, the spacing between the barriers61 and 62 and the mounting surface of the mounting board 53 becomesirregular.

[0009] As a result, although the inner and outer barriers 61 and 62 areprovided on the functional surface of the surface acoustic wave element52, the sealing resin 58 cannot be prevented from flowing in over thebarriers 61 and 62, and the sealing resin 58 reaches the vibratingportion 56 of the surface acoustic wave element 52 and may attach to thevibrating portion 56. When this occurs, degradation of the performanceof the surface acoustic wave device 51 is unavoidable and the rate ofdefective surface acoustic wave devices 51 increases.

SUMMARY OF THE INVENTION

[0010] In order to overcome the problems described above, preferredembodiments of the present invention provide a surface acoustic wavedevice in which a sealing resin for sealing a gap between a surfaceacoustic wave element and a mounting board can be surely prevented fromflowing in to reach a vibrating portion of the surface acoustic waveelement.

[0011] A surface acoustic wave device according to a first preferredembodiment of the present invention includes a surface acoustic waveelement having, on a functional surface thereof, a vibrating portionincluding at least one comb-shaped electrode portion disposed on apiezoelectric substrate, a mounting board, and a sealing resin. In thesurface acoustic wave device, the surface acoustic wave element and themounting board are connected through bumps so that the mounting surfaceof the mounting board and the functional surface of the surface acousticwave element face each other, the outer peripheral edge of the surfaceacoustic wave element is sealed by the sealing resin, and a vibrationspace is secured between the vibrating portion of the surface acousticwave element and the mounting surface of the mounting board. Also, anouter barrier disposed so as to enclose the bumps and the vibratingportion is provided on the functional surface of the surface acousticwave element and the outer barrier includes a level difference.

[0012] In the surface acoustic wave device according to a firstpreferred embodiment of the present invention, since the outer barrierincludes a level difference, the sealing resin can be prevented fromflowing in at the outer barrier, and accordingly, the occurrence ofdefect, which is caused when the sealing resin flows to the vibratingportion of the surface acoustic wave element, can be prevented.

[0013] A surface acoustic wave device according to a second preferredembodiment of the present invention includes a surface acoustic waveelement having, on a functional surface thereof, a vibrating portionincluding at least one comb-shaped electrode portion disposed on apiezoelectric substrate, a mounting board, and a sealing resin. In thesurface acoustic wave device, the surface acoustic wave element and themounting board are connected through bumps so that the mounting surfaceof the mounting board and the functional surface of the surface acousticwave element face each other, the outer peripheral edge of the surfaceacoustic wave element is sealed by the sealing resin, and a vibrationspace is secured between the vibrating portion of the surface acousticwave element and the mounting surface of the mounting board. Also anouter barrier disposed so as to enclose the bumps and the vibratingportion and an inner barrier disposed inside the bumps so as to enclosethe vibrating portion are provided on the functional surface of thesurface acoustic wave element.

[0014] In the surface acoustic wave device according to a secondpreferred embodiment of the present invention, since the outer barrierand the inner barrier are provided, even if the flow of the sealingresin cannot be blocked at the outer barrier, the sealing resin can beprevented from flowing in at the inner barrier, and accordingly, theoccurrence of defects, which are caused when the sealing resin flows tothe vibrating portion of the surface acoustic wave element, can beprevented.

[0015] It is desirable that the outer barrier is higher than the innerbarrier. In particular, it is desirable that the height of the outerbarrier is lower than the total height of the bumps after the surfaceacoustic wave element and the mounting board have been connected throughthe bumps and the electrode lands formed on the mounting surface of themounting board, and the height of the inner barrier is preferably lowerthan the height of the bumps after the surface acoustic wave element andthe mounting board have been connected through the bumps.

[0016] It is also desirable that at least the inner barrier is formed byusing a material that is inferior in wettability against the sealingresin to the functional surface of the surface acoustic wave element andthe mounting surface of the mounting board. Furthermore, it is desirablethat the inner barrier includes a first inner barrier and a second innerbarrier. In particular, it is desirable that the first inner barrier andthe second inner barrier have nearly the same height. At this time, itis desirable that the first inner barrier and the second inner barrierare formed by using the same material.

[0017] Furthermore, it is desirable that the outer barrier has a leveldifference. Moreover, in the surface acoustic wave device according to afirst or second preferred embodiment of the present invention, it isdesirable that the level difference in the outer barrier is formed by atleast one concave portion or by at least one convex portion.

[0018] A surface acoustic wave device according to a third preferredembodiment of the present invention includes a surface acoustic waveelement on the functional surface of which a vibrating portion includingat least one comb-shaped electrode portion disposed on a piezoelectricsubstrate, a mounting board, and a sealing resin. In the surfaceacoustic wave device, the surface acoustic wave element and the mountingboard are connected through bumps so that the mounting surface of themounting board and the functional surface of the surface acoustic waveelement face each other, the outer peripheral edge of the surfaceacoustic wave element is sealed by the sealing resin, and a vibrationspace is secured between the vibrating portion of the surface acousticwave element and the mounting surface of the mounting board. Also afirst outer barrier disposed so as to enclose the bumps and thevibrating portion and a second outer barrier disposed inside the firstouter barrier so as to enclose the bumps and the vibrating portion areprovided on the functional surface of the surface acoustic wave element.

[0019] In the surface acoustic wave device according to a thirdpreferred embodiment of the present invention, since the first outerbarrier and the second outer barrier are provided, even if the flow ofthe sealing resin cannot be blocked at the first outer barrier, thesealing resin can be prevented from flowing in at the second outerbarrier, and accordingly, the occurrence of defects, which are causedwhen the sealing resin flows to the vibrating portion of the surfaceacoustic wave element, can be prevented.

[0020] It is desirable that the first outer barrier is higher than thesecond outer barrier. In particular, it is desirable that the height ofthe first outer barrier is lower than the total height of the bumpsafter the surface acoustic wave element and the mounting board have beenconnected through the bumps and the electrode lands provided on themounting surface of the mounting board, and the height of the secondouter barrier is preferably higher than the height of the bumps afterthe surface acoustic wave element and the mounting board have beenconnected through the bumps.

[0021] Also, it is desirable that the first outer barrier is made of atleast two layers, and the lowest layer of the first outer barrier hasthe same height as the second outer barrier. Furthermore, it isdesirable that at least the second outer barrier is formed by using amaterial that is inferior in wettability against the sealing resin tothe functional surface of the surface acoustic wave element and themounting surface of the mounting board. In this case, it is desirablethat the first outer barrier includes a level difference, and it isdesirable that the level difference in the first outer barrier is formedby at least one concave portion or by at least one convex portion.

[0022] Alternatively, in the surface acoustic wave device according to afirst, second, and third preferred embodiments of the present invention,it is desirable that a board-side barrier is arranged on the mountingboard so as to face the outer barrier. In particular, it is desirablethat the total height of the outer barrier and the board-side barrier islower than the total height of the bumps after the surface acoustic waveelement and the mounting board have been connected through the bumps andthe electrode lands formed on the mounting surface of the mountingboard.

[0023] Other features, elements, characteristics and advantages of thepresent invention will be apparent from the detailed description ofpreferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a transverse sectional view showing the structure of asurface acoustic wave device according to a first preferred embodimentof the present invention.

[0025]FIG. 2 is a top view showing the structure of a mounting boardaccording to the first preferred embodiment of the present invention.

[0026]FIG. 3 is a top view showing the structure of a surface acousticwave element according to the first preferred embodiment of the presentinvention.

[0027]FIG. 4 is a transverse sectional view showing the structure of asurface acoustic wave device according to a first modified example ofthe first preferred embodiment of the present invention.

[0028]FIG. 5 is a transverse sectional view showing the structure of asurface acoustic wave device according to a second modified example ofthe first preferred embodiment of the present invention.

[0029]FIG. 6 is a transverse sectional view showing the structure of asurface acoustic wave device according to a third modified example ofthe first preferred embodiment of the present invention.

[0030]FIG. 7 shows the manufacturing process of the surface acousticwave element according to the first preferred embodiment of the presentinvention.

[0031]FIG. 8 shows the manufacturing process of the surface acousticwave device according to the first preferred embodiment of the presentinvention.

[0032]FIG. 9 is a transverse sectional view showing the structure of asurface acoustic wave element according to a second preferred embodimentof the present invention.

[0033]FIG. 10 is a top view showing the structure of a surface acousticwave element according to the second preferred embodiment of the presentinvention.

[0034]FIG. 11 is a top view showing the structure of a mounting boardaccording to the second preferred embodiment of the present invention.

[0035]FIG. 12 shows the manufacturing process of the surface acousticwave element according to the second preferred embodiment of the presentinvention.

[0036]FIG. 13 shows the manufacturing process of a surface acoustic wavedevice according to the second preferred embodiment of the presentinvention.

[0037]FIG. 14 is a transverse sectional view showing the structure of asurface acoustic wave device according to a third preferred embodimentof the present invention.

[0038]FIG. 15 is a top view showing the structure of a surface acousticwave element according to the third preferred embodiment of the presentinvention.

[0039]FIG. 16 is a transverse sectional view showing the structure of asurface acoustic wave device according to a modified example of thethird preferred embodiment of the present invention.

[0040]FIG. 17 is a transverse sectional view showing the structure of asurface acoustic wave device according to a fourth preferred embodimentof the present invention.

[0041]FIG. 18 is a top view showing the structure of a surface acousticwave element according to the fourth preferred embodiment of the presentinvention.

[0042]FIG. 19 is a transverse sectional view showing the structure of asurface acoustic wave device according to a first modified example ofthe fourth preferred embodiment of the present invention.

[0043]FIG. 20 is a transverse sectional view showing the structure of asurface acoustic wave device according to a second modified example ofthe fourth preferred embodiment of the present invention.

[0044]FIG. 21 is a transverse sectional view showing the structure of asurface acoustic wave device according to a related example.

[0045]FIG. 22 is a top view showing the structure of a surface acousticwave element according to a related example.

[0046]FIG. 23 is a top view showing the structure of a mounting boardaccording to a related example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] First Preferred Embodiment

[0048]FIG. 1 is a transverse sectional view showing the structure of asurface acoustic wave device according to the first preferredembodiment, FIG. 2 is a top view showing the structure of a mountingboard according to first preferred embodiment, and FIG. 3 is a top viewshowing the structure of a surface acoustic wave element according tothe first preferred embodiment. FIG. 4 is a transverse sectional viewshowing the structure of a surface acoustic wave device according to afirst modified example, FIG. 5 is a transverse sectional view accordingto a second modified example, and FIG. 6 is a transverse sectional viewaccording to a third modified example. FIG. 7 shows the manufacturingprocess of the surface acoustic wave element according to firstpreferred embodiment, and FIG. 8 shows the manufacturing process of asurface acoustic wave device.

[0049] In a surface acoustic wave device 1 according to the firstpreferred embodiment, as shown in FIG. 1, the functional surface of asurface acoustic wave element (SAW device chip) 2 and the mountingsurface of a mounting substrate 3 are arranged so as to face each otherand are connected to each other through bumps 4 made of gold, and theouter peripheral edge of the surface acoustic wave element 2 is sealedby a sealing resin 5 which includes a thermosetting resin such as epoxyresin, etc. Then, a vibration space 7, which is required to generate asurface acoustic wave, is secured between the functional surface of thesurface acoustic wave element 2, that is, a vibrating portion 6 of thesurface acoustic wave element 2 including an IDT, reflector, and wiringportion provided on a piezoelectric substrate, and the mounting surfaceof the mounting board 3 made of a dielectric material such as alumina,etc. Moreover, on the mounting surface of the mounting board 3, as shownin FIG. 2, electrode lands 8 are provided at fixed locations so that thebumps 4 may be connected at fixed locations. The IDT, reflector, andwiring portion of the surface acoustic wave element 2 in FIG. 3 areomitted. The electrode lands 8 may have a different shape from that inFIG. 2.

[0050] On the other hand, on the functional surface of the surfaceacoustic wave element 2, an outer barrier 9 that blocks the resin flowand an inner barrier 10 that blocks the resin flow are provided so thatthe sealing resin 5 for sealing a gap between the surface acoustic waveelement 2 and the mounting board 3 may be prevented from flowing to thevibrating portion 6 of the surface acoustic wave element 2. That is, asshown in FIG. 3, on the functional surface of the surface acoustic waveelement 2, the outer barrier 9, which is disposed at an outer locationof the piezoelectric substrate to enclose both the bumps 4 and thevibration portion 6 and has a substantially rectangular shape whenviewed from the top, and the inner barrier 10, which is at an innerlocation to enclose only the vibrating portion 6 and has a substantiallyrectangular shape when viewed from the top, are provided. Moreover, thecorner portions of the outer barrier 9 and the inner barrier 10 may bemade substantially round.

[0051] The outer barrier 9 and the inner barrier 10 are preferablyformed by a photoresist method using a material that is inferior inwettability against the sealing resin 5 compared to the functionalsurface of the surface acoustic wave element 2 and the mounting surfaceof the mounting board 3, for example, a photosensitive polyimide resin,BCB (resin component: benzocyclobutene), Zcoat (resin component: cyclicpolyolefin), etc. Here, the outer barrier 9 has a double-layer structurein which a lower layer 9 a and an upper layer 9 b are laminated.

[0052] Although it is desirable that the material used in the outerbarrier 9 and the inner barrier 10 be excellent in heat resistanceduring reflow when the surface acoustic wave device 1 is mounted on aprinted circuit board by using solder, the reflow temperature isdependent on the solder material. For example, the reflow temperature ofa eutectic solder material of Sn—Pb is 180° C. and the reflowtemperature of a solder material of Sn—Ag—Cu is 220° C. When these aretaken into consideration, it is sufficient for the material used in theouter barrier 9 and the inner barrier 10 to withstand a temperature ofabout 260° C.

[0053] That is, the material for forming the outer barrier 9 and theinner barrier 10 preferably has the following characteristics. First,regarding the heat resistance to the reflow when mounting by soldering,it is required that no remarkable deformation, decomposition, andoutgassing be caused. However, after sealing by the sealing resin 5, thecondition that no deformation be caused is not necessarily required.

[0054] Next, in order to prevent the inflow of the sealing resin 5, itis desirable that the material for forming the barriers 9 and 10 beinferior in wettability against the sealing resin 5 to the surface ofthe piezoelectric substrate of the surface acoustic wave element 2 andthe mounting board 3 and to the surface of the electrode lands 8, etc.,disposed on the mounting board 3. Furthermore, the material for formingthe barriers 9 and 10 is required to have a low dielectric constant. Ifthe material has a large dielectric constant, the electrical properties,the input capacitance in particular, are changed by the disposition ofthe inner and outer barriers 9 and 10 and, as a result, thecharacteristics of the surface acoustic wave device 1 may bedeteriorated. Accordingly, it is desirable that the inner and outerbarriers 9 and 10 have a dielectric constant lower than that of thepiezoelectric substrate of the surface acoustic wave element 2.Moreover, after the barriers 9 and 10 have been formed, they arerequired to have a hardness which does not allow their deformation.Furthermore, in order to eliminate the deformation of a surface acousticwave caused by the difference in linear expansion coefficient betweenthe surface acoustic wave element 2 and the mounting board 3, a lowerhardness is desired.

[0055] On the other hand, in order to cope with changes in temperature,the material for forming the barriers 9 and 10 preferably has nearly thesame linear expansion coefficient as that of the piezoelectric substrateof the surface acoustic wave element 2. For example, when the substrateis made of LiTaO₃, since the linear expansion coefficient is about 15ppm/° C. in the propagation direction of a surface acoustic wave andabout 7 ppm/° C. in the direction perpendicular to the propagationdirection of the surface acoustic wave, it is desirable that the linearexpansion coefficients of the material for forming the barriers 9 and 10be close to these coefficients. Moreover, in order to prevent the innerbarrier 10 from coming into contact with the vibrating portion 6, it isdesirable that the linear expansion coefficient of the inner barrier 10be lower than that of the bumps 4.

[0056] Furthermore, the barriers 9 and 10 are preferably made of amaterial which makes it possible for the height of the barriers 9 and 10from the piezoelectric substrate of the surface acoustic wave element 2to be constant. That is, since the minimum width of the barriers 9 and10 is tens of micrometers, it is desirable to use a photosensitive resinin order to form the barriers 9 and 10 at a fixed location precisely.When there are local variations in height, since the spacing becomesuneven, a material having small bumps and dips and also having smallparticles in size is desirable. Moreover, after the barriers 9 and 10have been formed, since, for example, a cleaning process, a coatingprocess of the sealing resin, and a heating process are performed, it isrequired that the material withstand these processes and also havechemical resistance so that the material can withstand the compounds inthe sealing resin 5.

[0057] The height h1 of the outer barrier 9 is preferably lower than thetotal height h4 (=h2+h3) of the height h2 of the bumps 4 after beingconnected and the height h3 of the electrode lands 8 disposed on themounting surface of the mounting board 3, and the height h5 of the innerbarrier 10 is preferably lower than the height h2 of the bumps 4 afterbeing connected. At this time, since the height h1 of the outer barrier9 is preferably lower than the total height h4 of the height h2 of thebumps 4 after being connected and the height h3 of the electrode lands 8disposed on the mounting surface of the mounting board 3, a small gap issecured between the outer barrier 9 and the mounting surface of themounting board 3.

[0058] Moreover, when the height h1 of the outer barrier 9 is higherthan the total height h4 of the height h2 of the bumps 4 after beingconnected and the height h3 of the electrode lands 8 disposed on themounting surface of the mounting board 3, since the bumps 4 cannot bepressed as much as the thickness (height) of the outer barrier 9, asufficient connecting strength cannot be obtained when the mountingboard 3 and the surface acoustic wave element 2 are connected. That is,when the surface acoustic wave element 2 is flip-chip bonded to themounting board 3, in order to obtain a sufficient connecting strength ofthe pressed bumps 4, it is required to secure a gap S between the outerbarrier 9 and the mounting board 3 and, in the present preferredembodiment in which the height h1 of the outer barrier 9 is preferablylower than the total height h4 of the height h2 of the bumps 4 afterbeing connected and the height h3 of the electrode lands 8 disposed onthe mounting surface of the mounting board 3, since the gap S can besecured between the outer barrier 9 and the mounting surface of themounting board 3, a sufficient connecting strength can be obtained.

[0059] It is desirable that the gap S between the outer barrier 9 andthe mounting surface of the mounting board 3 be about 0 to about 15 μm.Furthermore, when the height h5 of the inner barrier 10 is lower thanthe height h2 of the bumps 4 after being connected, the inner barrier 10can be prevented from coming into contact with the electrode lands 8disposed on the mounting surface of the mounting board 3. Moreover, ifthe height h5 of the inner barrier 10 is higher than the height h2 ofthe bumps 4 after being connected, the inner barrier 10 comes intocontact with the electrode lands 8 of the mounting board 3 and, sincethe bumps 4 cannot be pressed, it becomes difficult to obtain asufficient connecting strength between the mounting board 3 and thesurface acoustic wave element 2.

[0060] Furthermore, the height h5 of the inner barrier 10 can be reducedby making the width of the barrier 10 larger than the spreading width ofthe sealing resin 5. Furthermore, when the outer barrier 9 is a laminateof a lower layer 9 a and an upper layer 9 b, it is desirable that thelower layer 9 a and the inner barrier 10 have the same height h5. Inthis way, the lower layer 9 a of the outer barrier 9 and the innerbarrier 10 can be formed in the same process and, since the outerbarrier 9 made of the lower layer 9 a and the upper layer 9 b is formedin two separate processes, the outer barrier 9 can be formed with a highaspect ratio.

[0061] In the surface acoustic wave device 1 according to the presentpreferred embodiment, the outer barrier 9 on the functional surface ofthe surface acoustic wave element 2 is provided outside the bumps 4 andthe above-described relationship among the heights is adopted. As aresult, the outer barrier 9 faces the mounting board 3 itself, that is,the exposed mounting board 3 in which the electrode lands 8 are notformed, and a gap S having a uniform spacing of (h4−h1) is securedbetween the outer barrier 9 and the mounting surface of the mountingboard 3. Therefore, even if the sealing resin 5 for sealing the outerperipheral edge of the surface acoustic wave element 2 reaches the outerbarrier 9, since the gap S between the outer barrier 9 and the mountingsurface of the mounting board 3 has a uniform spacing, the inflow of thesealing resin 5 across the outer barrier 9 does not occur.

[0062] Then, even if the sealing resin 5 flows in across the outerbarrier 9, since the inner barrier 10 having the height h5, which islower than the height h2 of the bumps 4 after being connected, isprovided so as to enclose the vibrating portion 6, a small quantity ofthe sealing resin 5 flowing over the outer barrier 9 can be surelyprevented from flowing in so as to reach the vibrating portion 6 of thesurface acoustic wave element 2 over the inner barrier 10. Furthermore,at this time, when the inner barrier 10 is made of a material that isinferior in wettability against the sealing resin 5, low molecularcomponents in the sealing resin 5, which are difficult for the outerbarrier 9 to prevent from flowing in, can be surely prevented fromflowing in onto the functional surface of the surface acoustic waveelement 2.

[0063] Moreover, in the present preferred embodiment, although the outerbarrier 9 is disposed so as to enclose the all bumps 4 and the innerbarrier 10 is disposed to enclose only the vibrating portion 6, it isnot limited to such a structure. The outer barrier 9 is disposed so asto enclose a portion of the bumps 4 and the vibrating portion 6 and theinner barrier 10 may enclose at least the vibrating portion 6. That is,it is enough for the outer barrier 9 to be disposed so as to face themounting surface of the mounting board 3 and, as a result, it is enoughthat a gap S having a uniform spacing is secured between the outerbarrier 9 and the mounting surface of the mounting board 3.

[0064] Here, it is enough for the inner barrier 10 to be able to preventthe sealing resin 5 coming over the outer barrier 9 from flowing to thevibrating portion 6 of the surface acoustic wave element 2, and it isenough for the inner barrier 10 to be disposed to enclose at least thevibrating portion 6. Furthermore, in the present preferred embodiment,although the outer barrier 9 and the inner barrier 10 are formed byusing a material that is inferior in wettability against the sealingresin 5, both of these are not required to be inferior in wettabilityagainst the sealing resin 5. That is, since a material inferior inwettability against the sealing resin 5 is particularly effective inpreventing the inflow of low molecular components in the sealing resin5, when the inner barrier 10 where the inflow of the sealing resin 5 isrequired to be surely prevented is inferior in wettability against thesealing resin 5, a regular photoresist material may be used for formingthe outer barrier 9.

[0065] Moreover, when the outer barrier 9 disposed on the functionalsurface of the surface acoustic wave element 2 includes a laminate ofthe lower layer 9 a and the upper layer 9 b, the lower layer 9 a may beformed by using the same metal material as the vibrating portion 6 ofthe surface acoustic wave element 2, that is, the IDT, etc. However, theouter barrier 9 is not required to be a laminate and, as shown in FIG.4, the outer barrier 9 may be integrally formed as a barrier having theheight h1 from the beginning.

[0066] Moreover, in the present preferred embodiment, as shown in FIG.1, only the outer peripheral edge of the surface acoustic wave element 2is sealed by the sealing resin 5 and the top surface of the surfaceacoustic wave element 2 is exposed to the outside, but it is not limitedto such a structure, and not only the outer peripheral edge of theacoustic wave element 2, but also the top surface may be sealed by thesealing resin 5. Moreover, it is desirable that the sealing resin 5 havea viscosity of about 15 Pa·s to about 150 Pa·s under the temperature atcoating and, when the sealing resin 5 has such a viscosity, the inflowof the sealing resin 5 can be more securely prevented. That is, when thesealing resin 5 has a low viscosity, the inflow becomes more likely tooccur and, when the sealing resin 5 has a high viscosity, since bubblesthat worsen the sealing property are likely to occur, the lower limit ofthe viscosity is determined by the inflow of the sealing resin 5 to thevibrating portion 6 and the upper limit is determined by the occurrenceof the bubbles.

[0067] Now, in the present preferred embodiment, it is possible to adoptthe following modified examples. First, as shown in FIG. 5, a stepportion may be formed in the outer barrier 9 by forming a groove(concave portion) 9 c having a fixed width in the outer barrier 9provided in the functional surface of the surface acoustic wave element2. When constructed in this way, even if the inflow of the sealing resin5 cannot be prevented at the outside corner portion of the outer barrier9, it becomes possible to prevent the inflow of the resin 5 at theinside corner portion. Moreover, when a step portion is provided byforming a convex portion in the outer barrier 9, the same effect canalso be obtained.

[0068] Furthermore, as shown in FIG. 6, between the outer barrier 9 andthe inner barrier 10, an outer barrier (second outer barrier) 11 may beprovided so as to be next to the outer barrier (first outer barrier) 9.When constructed in this way, even if the inflow of the sealing resin 5cannot be prevented by the outer barrier 9, it becomes possible toprevent the inflow of the sealing resin 5 by the outer barrier (secondouter barrier) 11.

[0069] Moreover, although not illustrated, a groove having a fixed widthmay be formed in the inner barrier 10 and, when constructed in this way,even if the size of the inner barrier 10 is not changed, the separatingdistance between the inner barrier 10 and the vibrating portion 6becomes large and, as a result, the sealing resin 5 does not reach thevibrating portion 6. Furthermore, a second inner barrier may be providedinside the inner barrier (first inner barrier) 10 so as to be next tothe inner barrier 10. When constructed in this way, since the separatingdistance between the inner barrier (first inner barrier) 10 and thevibrating portion 6 is increased by the second inner barrier, the inflowof the sealing resin 5 to the vibrating portion 6 can be securelyprevented.

[0070] Furthermore, in this case, it is desirable that the height of thesecond inner barrier be nearly the same as that of the inner barrier(first inner barrier) 10 and that the second inner barrier be formed byusing the same material as the inner barrier (first inner barrier) 10.That is, when constructed in this way, the second inner barrier can beformed in concurrence with the inner barrier (first inner barrier) 10.

[0071] Next, the manufacturing method for the surface acoustic wavedevice 1 and surface acoustic wave element 2 according to the firstpreferred embodiment is simply described based on FIGS. 7 and 8.

[0072] First, as shown in FIG. 7 in which a manufacturing process of asurface acoustic wave element is illustrated, a piezoelectric substrate12 (LiTaO₃ wafer) having a plurality of bumps 4 and vibrating portions 6(not illustrated), from which many surface acoustic wave elements 2 areproduced by dicing, is prepared and the outer barrier 9 and innerbarrier 10 are formed on each surface-acoustic-wave-element area 13where the bumps 4 and the vibrating portion have been formed. Moreover,the piezoelectric substrate 12 may be made of any other material such asLiNbO₃, instead of LiTaO₃.

[0073] Furthermore, it is possible to use a dielectric substrate on thesurface of which a piezoelectric thin film such as ZnO, etc., is formedcan be used instead of the piezoelectric substrate 12. Furthermore, inthe above description, although the outer barrier 9 and the innerbarrier 10 are formed on the surface-acoustic-wave-element area 13 wherethe bumps 4 are formed, the bumps 4 may be formed after the outerbarrier 9 and the inner barrier 10 have been formed.

[0074] That is, on the LiTaO₃ wafer as the piezoelectric substrate 12having the vibrating portion 6 of the IDT, reflector, etc., formedthereon, the lower layer 9 a of the outer barrier 9 disposed so as toenclose the bumps 4 and the vibrating portion 6 and the inner barrier 10disposed to enclose only the vibrating portion 6 are simultaneouslyformed by a photoresist method so that the height h5 may be lower thanthe height h2 of the bumps 4 after being connected. Next, the upperlayer 9 b is laminated on the lower layer 9 a of the outer barrier 9 soas to define a height (h1−h5) which is higher than the height h3 of theelectrode lands 8 formed on the mounting surface of the mounting board3.

[0075] As a result, in each surface-acoustic-wave-element area 13 in thepiezoelectric substrate 12, the outer barrier 9 having the height h1which encloses the bumps 4 and the vibrating portion 6 and the innerbarrier 10 having the height h5 which encloses only the vibratingportion 6 are formed. After that, when the LiTaO₃ wafer as thepiezoelectric substrate 12 is diced into chip-sized pieces, a surfaceacoustic wave element 2 corresponding to eachsurface-acoustic-wave-element area is produced.

[0076] Now, when an outer barrier (second outer barrier) 11 is providedbetween the outer barrier (first outer barrier) 9 and the inner barrier10 provided on the functional surface of the acoustic wave element 2,and when a second inner barrier is provided inside the inner barrier(first inner barrier) 10, the outer barrier (second outer barrier) 11and second inner barrier are formed together with the outer barrier(first outer barrier) 9 and inner barrier (first inner barrier) 10 oneach surface-acoustic-wave-element area 13 of the piezoelectricsubstrate 12.

[0077] Furthermore, electrode lands 8 are formed in advance on an areacorresponding to each of the surface acoustic wave elements 2, that is,on an area 14 corresponding to the element, and thus a compositesubstrate 15 from which the mounting board 3 is produced later isprepared. Then, as shown in FIG. 8, each of the surface acoustic waveelements 2 which were produced by dicing is flip-chip bonded and mountedon an area 14 corresponding to the element. After that, although notillustrated, a sealing resin 5 is coated and hardened around eachsurface acoustic element 2 mounted on a composite substrate 15 and thecomposite substrate 15 is diced to chip-size pieces to produce a surfaceacoustic wave device 1 having the structure shown in FIG. 1.

[0078] Second Preferred Embodiment

[0079]FIG. 9 is a transverse sectional view showing the structure of asurface acoustic wave device according to a second preferred embodiment,FIG. 10 is a top view showing the structure of a surface acoustic waveelement, and FIG. 11 is a top view showing the structure of a mountingboard. FIG. 12 shows the manufacturing process of the surface acousticwave element of the second preferred embodiment and FIG. 13 shows themanufacturing process of a surface acoustic wave device. Moreover, sincethe whole structure of the surface acoustic wave device according tosecond preferred embodiment is basically not different from the firstpreferred embodiment, in FIGS. 9 to 13, the same elements as orequivalent ones to those in FIGS. 1 to 8 are given the same referencenumerals and their detailed description is omitted.

[0080] In a surface acoustic wave device 21 according to secondpreferred embodiment, as shown in FIG. 9, the functional surface of thesurface acoustic wave element (SAW device chip) 2 is connected to themounting surface of the mounting board 3 through the bumps 4 and onlythe outer peripheral edge of the surface acoustic wave element 2 issealed. A vibration space 7 is secured between the vibrating portion 6formed on the functional surface of the surface acoustic wave element 2,that is, the vibrating portion 6 of the surface acoustic wave element 2which includes the IDT, reflector, and wiring portion, and the mountingsurface of the mounting board 3 made of a dielectric material such asalumina, etc. Moreover, the IDT, reflector, and wiring portion of thesurface acoustic wave element 2 in FIG. 10 are schematically shown.Thus, these actual shapes may be different from those in the drawing.

[0081] Furthermore, on the functional surface of the surface acousticwave element 2, as shown in FIG. 10, both an outer barrier 22 and aninner barrier 23 are provided inside and outside in order to prevent thesealing resin 5 such as an epoxy resin, etc., which seals a gap betweenthe surface acoustic wave element 2 and the mounting surface of themounting board 3, from flowing to the vibrating portion 6 of the surfaceacoustic wave element 2. That is, on the functional surface of thesurface acoustic wave element 2, an outer barrier 22 disposed at anouter location which encloses the bumps 4 and the vibrating portion 6and having a substantially rectangular shape when viewed from the topand an inner barrier 23 disposed at an inner location which enclosesonly the vibrating portion 6 and having a substantially rectangularshape when viewed from the top are provided. Moreover, the outer barrier22 preferably has the same height h5 as that of the inner barrier 23 andh5 is preferably lower than the height h2 of the bumps 4 after beingconnected (h5<h2).

[0082] On the other hand, on the mounting surface of the mounting board3, as shown in FIG. 11, electrode lands for connecting the bumps 4 aredisposed at fixed locations, and a board-side barrier 24 is arranged soas to enclose the bumps 4 and the vibrating portion 6 on the functionalsurface of the surface acoustic wave element 2 is arranged to face theouter barrier 22 formed in the surface acoustic wave element 2.Furthermore, the height h6 of the board-side barrier 24 is preferablyset such that the total height h7 (=h5+h6) of the height h5 of the outerbarrier 22 and the height h6 of the board-side barrier 24 is lower thanthe total height h4 (=h2+h3) of the height h2 of the bumps 4 after beingconnected and the height h3 of the electrode lands 8 formed on themounting surface of the mounting board 3.

[0083] Since the outer barrier 22, the inner barrier 23, and theboard-side barrier 24 have the above-described relationship among theheights, a gap S having a uniform spacing of (h4−h7) is secured betweenthe outer barrier 22 disposed on the functional surface of the surfaceacoustic wave element 2 and the board-side barrier 24 disposed on themounting surface of the mounting board 3. As a result, even if the bumps4 are pressed when the surface acoustic wave element 2 is flip-chipbonded to the mounting board 3, the outer barrier 22 and the board-sidebarrier 24, which are arranged so as to face each other, do not comeinto contact with each other and it becomes possible to obtain asufficient connecting strength for the bumps 4.

[0084] In the surface acoustic wave device 21, even if the sealing resin5 for sealing the outer peripheral edge of the surface acoustic waveelement 2 reaches the outer barrier 22 and the board-side barrier 24,since the gap S between the outer barrier 22 and the board-side barrier24 is uniform, the sealing resin does not flow in over the outer barrier22 and the board-side barrier 24. Furthermore, even if the sealing resin5 flows in over the outer barrier 22 and the board-side barrier 24,since the inner barrier 23 encloses the vibration portion 6 of thesurface acoustic wave element 2, a small quantity of the sealing resin 5which comes over the outer barrier 22 is securely prevented from flowingto the vibrating portion 6.

[0085] Moreover, it is desirable that the gap S between the outerbarrier 22 and the mounting board 3 be about 0 to about 15 μm. That is,although the outer barrier 22 comes partially in contact with themounting board 3 because of the bending and tilting of the mountingboard 3, the inflow of the sealing resin 5 can be prevented by settingthe average spacing of the gap S to the above value.

[0086] Furthermore, it is desirable that, among the outer barrier 22,the inner barrier 23, and the board-side barrier 24, at least the innerbarrier 23 is formed by using a material that is inferior in wettabilityagainst the sealing resin 5 to the functional surface of the surfaceacoustic wave element 2 and the mounting surface of the mounting board3, for example, a photoresist polyimide, etc., as in the first preferredembodiment. When constructed in this way, it becomes possible for lowmolecular components in the sealing resin 5, which were difficult toprevent from flowing in by the outer barrier 22 and the board-sidebarrier 24, to be reliably prevented from flowing along the functionalsurface of the surface acoustic wave element 2.

[0087] A material that is inferior in wettability against the sealingresin 5 is effective in preventing low molecular components in thesealing resin 5 from flowing in, and, when the inner barrier 23, whichis required to reliably prevent the sealing resin 5 from flowing in, ismade of a material inferior in wettability against the sealing resin 5,the outer barrier 22 and the board-side barrier 24 are not necessarilyrequired to be inferior in wettability against the sealing resin 5.Therefore, when the inner barrier 23, which is required to surelyprevent the sealing resin 5 from flowing in, is inferior in wettabilityagainst the sealing resin 5, regular photoresist materials may be usedto form the outer barrier 22. Furthermore, a material for forming theouter barrier 22, the inner barrier 23, and the board-side barrier 24that is excellent in heat resistance (260° C.) during reflow isdesirable.

[0088] Now, although not illustrated, also in the second preferredembodiment, the same modifications as in the first preferred embodimentcan be adopted. That is, the outer barrier 22 provided on the functionalsurface of the surface acoustic wave element 2 is disposed so as toenclose some of the bumps 4 and the vibrating portion 6, and the innerbarrier 23 may be disposed so as to enclose at least the vibratingportion 6. Furthermore, a groove is formed in each of the outer barrier22 and the inner barrier 23, a second outer barrier is provided betweenthe outer barrier 22 and the inner barrier 23, and a second innerbarrier may be provided inside the inner barrier 23.

[0089] Next, the manufacturing method for the surface acoustic wavedevice 21 and surface acoustic wave element 2 according to the presentpreferred embodiment is simply described based on FIGS. 12 and 13.

[0090] First, as shown in FIG. 12 in which the manufacturing process ofa surface acoustic wave element is illustrated, a piezoelectricsubstrate 12 (LiTaO₃ wafer) having a plurality of bumps 4 and vibratingportions 6 (not illustrated), from which many surface acoustic waveelements 2 are produced by dicing, is provided, and the outer barrier 22and the inner barrier 23 are formed on eachsurface-acoustic-wave-element area where the bumps 4 and the vibratingportion 6 are formed. Moreover, a substrate made of not only LiTaO₃, butalso LiNbO₃, etc., may be used as the piezoelectric substrate 12.

[0091] Furthermore, although the piezoelectric substrate 12 is usedhere, instead of the piezoelectric substrate 12, it is possible to use adielectric substrate on which a piezoelectric thin film of ZnO, etc., isformed. Moreover, although the outer barrier 22 and the inner barrier 23are formed in a surface-acoustic-wave-element area where the bumps 4 areformed, a process in which the bumps 4 are formed after the outerbarrier 22 and the inner barrier 23 have been formed may be used.

[0092] That is, on the LiTaO₃ wafer as the piezoelectric substrate 12 onwhich the vibrating portion 6 made of the IDT and the reflector isformed, the outer barrier 22 disposed so as to enclose the bumps 4 andthe vibrating portion 6 and the inner barrier 23 disposed to encloseonly the vibrating portion 6 are simultaneously formed by a photoresistmethod using a photosensitive polyimide resin, etc., so that the heighth5 of the barriers 22 and 23 may be lower than the height h2 of thebumps 4 after being connected.

[0093] Next, the LiTaO₃ wafer as the piezoelectric substrate 12 is dicedinto chip-size pieces and surface acoustic wave elements 2 correspondingto surface-acoustic-wave-element areas, respectively, are produced. Onthe other hand, electrode lands 8 are formed in advance in an areacorresponding to each surface acoustic wave element 2, that is, an area14 corresponding to the element, and a composite substrate 15, fromwhich mounting substrates 3 are produced later, is prepared and, asshown in FIG. 13, a board-side barrier 24 is formed at a location facingthe outer barrier 22 at each area 14 corresponding to the element of thecomposite substrate 15, that is, at a location facing the outer barrier22 formed in the surface acoustic wave element 2.

[0094] After that, each surface acoustic wave element 2 produced bydicing is mounted at each area 14 corresponding to the element of thecomposite substrate 15 by flip-chip bonding. Next, although notillustrated, after the sealing resin 5 has been coated around eachsurface acoustic wave element 2 mounted on the composite substrate 15and hardened, when the composite substrate 15 is diced and divided intochip-size pieces, the surface acoustic wave device 21 having thestructure shown in FIG. 9 is provided.

[0095] Third Preferred Embodiment

[0096]FIG. 14 is a transverse sectional view showing the structure of asurface acoustic wave device according to third preferred embodiment,FIG. 15 is a top view showing the structure of a surface acoustic waveelement, and FIG. 16 is a transverse sectional view showing thestructure of a surface acoustic wave device according to a modifiedexample of third preferred embodiment. Moreover, since the wholestructure of the surface acoustic wave device according to thirdpreferred embodiment is basically not different from the first preferredembodiment, in FIGS. 14 to 16, the same elements as or equivalent onesto those in FIGS. 1 to 8 are given the same reference numerals and theirdetailed description is omitted.

[0097] In a surface acoustic wave device 31 according to third preferredembodiment, as shown in FIG. 14, the functional surface of the surfaceacoustic wave element (SAW device chip) 2 is connected to the mountingsurface of the mounting board 3 through the bumps 4, and the outerperipheral edge and top surface of the surface acoustic wave element 2are sealed by the sealing resin 5. A vibration space 7 is securedbetween the vibrating portion 6 disposed on the functional surface ofthe surface acoustic wave element 2, that is, the vibrating portion 6 ofthe surface acoustic wave element 2 which includes the IDT, reflector,and wiring portion, and the mounting surface of the mounting board 3made of a dielectric material such as alumina, etc. Moreover, the IDT,reflector, and wiring portion of the surface acoustic wave element 2 inFIG. 15 are schematically shown. Thus, these actual shapes may bedifferent from those in the drawing.

[0098] On the other hand, on the mounting surface of the mounting board3, as shown in FIG. 14, the electrode lands 8 for connecting the bumps 4at fixed locations are disposed at fixed locations. Furthermore, on thefunctional surface of the surface acoustic wave element 2, as shown inFIG. 15, an outer barrier 32 which prevents the sealing resin 5 forsealing the space between the surface acoustic wave element 2 and themounting board 3, for example, the sealing resin 5 composed of epoxyresin, etc., from flowing to the vibrating portion 6 of the surfaceacoustic wave element 2 is provided. That is, on the functional surfaceof the surface acoustic wave element 2, the outer barrier 32 having asubstantially rectangular shape when viewed from the top is provided soas to enclose the bumps 4 and the vibrating portion 6.

[0099] The outer barrier 32 is formed by a photoresist method using amaterial that is inferior in wettability against the sealing resin 5 tothe functional surface of the surface acoustic wave element 2 and themounting surface of the mounting board 3, for example, a photosensitivepolyimide resin, BCB (resin component: benzocyclobutene), Zcoat (resincomponent: cyclic polyolefin), etc. Then, it is desirable that thematerial used in the outer barrier 32 be excellent in heat resistanceduring reflow when the surface acoustic wave device 1 is mounted on aprinted circuit board.

[0100] Moreover, the reflow temperature is dependent on the soldermaterial. For example, the reflow temperature of a eutectic soldermaterial of Sn—Pb is 180° C. and the reflow temperature of a soldermaterial of Sn—Ag—Cu is 220° C. When these facts are considered, it issufficient for the material used in the outer barrier 32 to withstand atemperature of about 260° C. Furthermore, as shown in FIG. 14, the outerbarrier 32 here has a laminated structure of a lower layer 32 a and anupper layer 32 b. When constructed in this way, since the upper layer 32b can be formed after the lower layer 32 a has been formed, it becomespossible to form a barrier with a high aspect ratio compared with thatof a single-layer structure.

[0101] Furthermore, the outer barrier 32 is preferably lower than thetotal height of the bumps 4 after being connected and the electrodelands. Since the outer barrier 32 has the above-described height, a gapS having a uniform spacing is secured between the outer barrier 32formed on the functional surface of the surface acoustic wave element 2and the mounting surface of the mounting board 3. As a result, when thesurface acoustic wave element 2 is flip-chip bonded to the mountingboard 3, even if the bumps 4 are pressed, the outer barrier 32 does notcome in contact with the mounting board 3, even though both are arrangedso as to face each other, and a sufficient connecting strength of thebumps 4 can be obtained.

[0102] In the surface acoustic wave device 31, even if the sealing resin5 for sealing the outer peripheral edge of the surface acoustic waveelement 2 reaches the outer barrier 32, since the gap between the outerbarrier 32 and the mounting board 3 is uniform, the sealing resin 5 doesnot flow in over the outer barrier 32. Moreover, it is desirable thatthe gap S between the outer barrier 32 and the mounting board 3 be inthe range of about 0 to about 15 μm.

[0103] Now, as shown in FIGS. 14 and 15, the outer barrier 32 of thirdpreferred embodiment 3 has a groove (concave portion) 32 c having afixed width and, as a result, the outer barrier 32 has a step portion.Therefore, even if the inflow of the sealing resin is not prevented atthe outside step portion in the outer barrier 32, the inflow of thesealing resin can be prevented by the inside step portion.

[0104] That is, since there is a level difference in the outer barrier32 because of the groove 32 c, the principle of preventing the sealingresin 5 from flowing in is as follows. First, the sealing resin 5 iscoated from the direction of the outer peripheral edge of the surfaceacoustic wave element 2 and, when there is no level difference in theouter barrier 32, the sealing resin 5 flowing over the edge portion ofthe outer barrier 32 may reach the vibrating portion 6. On the otherhand, when there is a level difference in the outer barrier 32, even ifthe sealing resin 5 runs over the step portion of the outer barrier 32,the sealing resin 5 which runs over the outer barrier 32 reaches thebottom portion of the groove 32.

[0105] Then, the edge portion having the level difference has an effectand, because of the surface tension, the sealing resin 5 more easilyruns in the direction of the level difference rather than in thedirection of the vibrating portion 6. That is, the sealing resin 5 runsin the direction of the extending direction of the groove 32 c, but, nottoward the vibrating portion 6. Therefore, when the outer barrier 32having a level difference is provided, the sealing resin 5 can be moresecurely prevented from flowing in. Moreover, as shown in FIG. 16, evenif the step portion is provided in the outer barrier 32 by forming aconvex portion in the outer barrier 32, the same effect can be obtained.At this time, the step portion is not necessarily required to be atright angles, but may have a trailing or tapered angle which occurs inthe processing.

[0106] Furthermore, also in the present preferred embodiment, in thesame way as in the second preferred embodiment, it goes without sayingthat a board-side barrier may be provided at a location at which theboard-side barrier faces the outer barrier 32 on the mounting board 3.Moreover, it is desirable that the total height of the outer barrier 32and the board-side barrier be lower than the total height of the heightof the bumps 4 after the surface acoustic wave element 2 and themounting board 3 have been connected through the bumps 4 and the heightof the electrode lands 8 formed on the mounting surface of the mountingboard 3.

[0107] Fourth Preferred Embodiment

[0108]FIG. 17 is a transverse sectional view showing the structure of asurface acoustic wave device according to a fourth preferred embodiment,FIG. 18 is a top view showing the structure of a surface acoustic waveelement, FIG. 19 is a transverse sectional view showing the structure ofa surface acoustic wave device according to a first modified example ofthe fourth preferred embodiment, and FIG. 20 is a transverse sectionalview showing the structure of a surface acoustic wave device accordingto a second modified example of the fourth preferred embodiment. Sincethe whole structure of the surface acoustic wave device according to thefourth preferred embodiment is basically not different from the firstpreferred embodiment, in FIGS. 17 to 20, the same elements as orequivalent ones to those in FIGS. 1 to 8 are given the same referencenumerals and their detailed description is omitted.

[0109] In a surface acoustic wave device 41 according to the fourthpreferred embodiment, as shown in FIG. 17, the functional surface of thesurface acoustic wave element (SAW device chip) 2 is connected to themounting surface of the mounting board 3 through the bumps 4, and theouter peripheral edge and top surface of the surface acoustic waveelement 2 are sealed by using the sealing resin 5. Then, a vibrationspace 7 is secured between the vibrating portion 6 disposed on thefunctional surface of the surface acoustic wave element 2, that is, thevibrating portion 6 of the surface acoustic wave element 2 including theIDT, reflector, wiring portion, and pad portion, and the mountingsurface of the mounting board 3 made of a dielectric material such asalumina, etc. Moreover, the surface acoustic wave element 2 is notlimited to the one in which two IDTs are cascade connected.

[0110] On the mounting surface of the mounting board 3, as shown in FIG.17, the electrode lands 8 for connecting the bumps 4 at fixed locationsare formed at fixed locations. Furthermore, on the functional surface ofthe surface acoustic wave element 2, as shown in FIG. 18, a first outerbarrier 42 and a second outer barrier 43 are provided to prevent thesealing resin 5 for sealing the gap between the surface acoustic waveelement 2 and the mounting board 3, for example, the sealing resin 5such as an epoxy resin, etc., from flowing to the vibrating portion 6 ofthe surface acoustic wave element 2. That is, on the functional surfaceof the surface acoustic wave element 2, the first outer barrier 42disposed at an outer location which encloses the bumps 4 and thevibrating portion 6 and having a substantially rectangular shape whenviewed from the top and the second outer barrier 43 disposed inside thefirst outer barrier 42 and having a substantially rectangular shape whenviewed from the top are provided. Moreover, the corner portions of thefirst outer barrier 42 and the second outer barrier 43 may be rounded.

[0111] Accordingly, in the surface acoustic wave device 41, even if thesealing resin 5 for sealing the outer peripheral edge of the surfaceacoustic wave element 2 flows in over the first outer barrier 42, sincethe second outer barrier 43 is provided inside the first outer barrier42 so as to enclose the bumps 4 and the vibrating portion 6, lowmolecular components in the sealing resin 5 running over the first outerbarrier 42 are prevented from reaching the vibrating portion 6.Moreover, a protective film of SiO₂, etc., may be formed on the surfaceof the surface acoustic wave element 2.

[0112] At this time, the first outer barrier 42 and the second outerbarrier 43 are preferably formed by a photoresist method using amaterial that is inferior in wettability against the sealing resin 5 tothe functional surface of the surface acoustic wave element 2 and themounting surface of the mounting board 3, for example, a photosensitivepolyimide resin, BCB (resin component: benzocyclobutene), Zcoat (resincomponent: cyclic polyolefin), etc. Moreover, it is desirable that thematerial used for forming the first outer barrier 42 and the secondouter barrier 43 have excellent heat resistance to the reflow when thesurface acoustic wave device 1 is mounted on a printed circuit board byusing solder.

[0113] However, the reflow temperature is dependent on the soldermaterial to be used. For example, the reflow temperature of a eutecticmaterial of Sn—Pb is 180° C. and the reflow temperature of a soldermaterial of Sn—Ag—Cu is 220° C. When these are considered, it issufficient for the material used in the outer barrier 32 to withstand atemperature of about 260° C.

[0114] Furthermore, as shown in FIG. 17, the first outer barrier 42 hasa double-layer structure where a lower layer 42 a and an upper layer 42b are laminated. When constructed in this way, since the upper layer 42b can be formed on the lower layer 42 a which has been formed, a barrierhaving a higher aspect ratio can be formed when compared with asingle-layer barrier. Moreover, the lower layer 42 a of the first outerbarrier 42 and the second outer barrier 43 have the same height.Therefore, it becomes possible to form the lower layer 42 a of the firstouter barrier 42 and the second outer barrier 43 in the same process.

[0115] On the other hand, the height of the second outer barrier 43 ispreferably lower than the first outer barrier 42, and the first outerbarrier 42 is preferably lower than the total height of the bumps 4after being connected and the electrode lands. Since the first outerbarrier 42 and the second outer barrier 43 have the above-describedheights, a gap S having a uniform spacing can be secured between thefirst outer barrier 42 disposed on the functional surface of the surfaceacoustic wave element 2 and the mounting surface of the mounting board3.

[0116] As a result, even if the bumps 4 are pressed when the surfaceacoustic wave element 2 is flip-chip bonded to the mounting board 3, thefirst outer barrier 42 and the second outer barrier 43, which arearranged to face the mounting board 3, do not come into contact with themounting board 3, and it becomes possible to obtain a sufficientconnecting strength of the bumps 4. Therefore, in the surface acousticwave device 41, even if the sealing resin 5 for sealing the peripheraledge of the surface acoustic wave element 2 reaches the first outerbarrier 42, since the gap S between the first outer barrier 42 and themounting board 3 is uniform, the sealing resin 5 does not flow in overthe first outer barrier 42.

[0117] Moreover, it is desirable that the width of the gap S between thefirst outer barrier 42 and the mounting surface of the mounting board 3be about 0 to about 15 μm.

[0118] Furthermore, in the first outer barrier 42, as shown in FIGS. 17and 18, a groove (concave portion) 42 c having a fixed width is formed.As a result, the first outer barrier 42 has a level difference and, evenif the peripheral edge portion of the first outer barrier 42 cannotprevent the sealing resin 5 from flowing in, the edge portion locatedinside the peripheral edge portion can reliably prevent the sealingresin 5 from flowing in.

[0119] Here, the principle that the level difference due to the groove42 c formed in the first outer barrier 42 can prevent the sealing resin5 from flowing in is described. First, although the sealing resin 5 iscoated from the direction of the outer peripheral edge of the surfaceacoustic wave element 2, when there is no level difference in the firstouter barrier 42, the sealing resin 5 running over the edge portion ofthe first outer barrier 42 may reach the vibrating portion 6. However,when there is a level difference in the first outer barrier 42, as soonas the sealing resin 5 runs over the edge portion of the first outerbarrier 42, the sealing resin 5 running over the first outer barrier 42reaches the bottom portion of the groove 42 c which makes the leveldifference.

[0120] Therefore, the edge portion making the level difference has aneffect and, because of the surface tension, the sealing resin 5 easilyruns along the level difference, rather than toward the vibratingportion 6. That is, the sealing resin 5 does not run toward thevibrating portion 6, but the sealing resin 5 runs along the extendingdirection of the groove 42 c. Accordingly, it becomes possible toprevent the sealing resin 5 from flowing in by providing the outerbarrier 42 having the level difference. Moreover, as shown in FIG. 19,even if a level difference is provided by forming a convex portion inthe first outer barrier 42, the same effect can be obtained. Here, thelevel difference is not required to be at right angles, but the leveldifference may have a trailing and tapered angle which occurs in theprocessing.

[0121] Moreover, the structure of the present preferred embodiment hasthe following advantages. In the structure of the first and secondpreferred embodiments, since the inner barrier is disposed between theIDT portion and the bumps, the layout of the piezoelectric substrate inthe surface acoustic wave element becomes complicated. Thus, the wiringportion on the signal side and the wiring portion on the grounding sidecome close to each other and, as a result, the capacitance increases.Then, since the characteristics are likely to deteriorate, it isnecessary to increase the size of the piezoelectric substrate to avoidthe problem. However, since the inner barrier is not provided in thefourth preferred embodiment, it is not necessary to increase the size ofthe piezoelectric substrate. Furthermore, since the contact between theouter barrier (first outer barrier in the fourth preferred embodiment)and the IDT, reflector, and wiring portion on the piezoelectricsubstrate causes the inflow of the sealing resin, a gap of a fixedspacing is required between the IDT, reflector, wiring portion, etc., onthe piezoelectric substrate and the outer barrier in the fourthpreferred embodiment in consideration of variations in manufacturing,such as mounting accuracy of the surface acoustic wave element to themounting board, etc. In the fourth preferred embodiment, since thesecond outer barrier is disposed in an area between the IDT, reflector,wiring portion, etc., on the piezoelectric substrate and the outerbarrier (first outer barrier in the present Embodiment 4), even if thesecond outer barrier is added, it is not required to increase the sizeof the piezoelectric substrate.

[0122] In the present preferred embodiment, it is possible to adopt thefollowing modified example. That is, as shown in FIG. 20, the firstouter barrier 42 provided on the functional surface of the surfaceacoustic wave element 2 may not have any level difference. Also in thiscase, since the second outer barrier 43 is provided inside the firstouter barrier 42, even if the sealing resin 5 for sealing the outerperipheral edge of the surface acoustic wave element 2 flows in over thefirst barrier 42, the second outer barrier 43 can prevent low molecularcomponents of the sealing resin 5 running over the first outer barrier42 from flowing in to the vibrating portion 6.

[0123] However, as described above, when the first outer barrier 42 isformed to have the level difference, it goes without saying that thesealing resin 5 can be more assuredly prevented from flowing in.Furthermore, in the present preferred embodiment, in the same way as inthe second preferred embodiment, the board-side barrier may be providedat a location opposite to the first outer barrier 42 on the mountingboard 3. Moreover, it desirable that the total height of the first outerbarrier 42 and the board-side barrier be lower than the total height ofthe bumps 4 after the surface acoustic wave element 2 and the mountingboard 3 have been connected through the bumps 4 and the electrode landsformed on the mounting surface of the mounting board 3.

[0124] According to a surface acoustic wave device of various preferredembodiments of the present invention, the sealing resin for sealing agap between a surface acoustic wave element and a mounting board can besurely prevented from flowing in to reach the vibrating portion of thesurface acoustic wave element.

[0125] While the present invention has been described with respect topreferred embodiments, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically set out anddescribed above. Accordingly, it is intended by the appended claims tocover all modifications of the invention which fall within the truespirit and scope of the invention.

1-21. (canceled).
 22. A surface acoustic wave device comprising: asurface acoustic wave element having, on a functional surface thereof, avibrating portion including at least one comb-shaped electrode portiondisposed on a piezoelectric substrate; a mounting board; and a sealingresin; wherein the surface acoustic wave element and the mounting boardare connected through bumps so that a mounting surface of the mountingboard and the functional surface of the surface acoustic wave elementface each other, an outer peripheral edge of the surface acoustic waveelement is sealed by the sealing resin, and a vibration space is securedbetween the vibrating portion of the surface acoustic wave element andthe mounting surface of the mounting board; and an outer barrierdisposed so as to enclose the bumps and the vibrating portion isprovided on the functional surface of the surface acoustic wave elementand the outer barrier includes a level difference.
 23. A surfaceacoustic wave device comprising: a surface acoustic wave element having,on a functional surface thereof, a vibrating portion including at leastone comb-shaped electrode portion disposed on a piezoelectric substrate;a mounting board; and a sealing resin; wherein the surface acoustic waveelement and the mounting board are connected through bumps so that amounting surface of the mounting board and the functional surface of thesurface acoustic wave element face each other, an outer peripheral edgeof the surface acoustic wave element is sealed by the sealing resin, anda vibration space is secured between the vibrating portion of thesurface acoustic wave element and the mounting surface of the mountingboard; and an outer barrier disposed so as to enclose the bumps and thevibrating portion and an inner barrier disposed inside the bumps so asto enclose the vibrating portion are included on the functional surfaceof the surface acoustic wave element.
 24. A surface acoustic wave deviceas claimed in claim 23, wherein the outer barrier is higher than theinner barrier.
 25. A surface acoustic wave device as claimed in claim24, wherein the height of the outer barrier is lower than the totalheight of the bumps after the surface acoustic wave element and themounting board have been connected through the bumps and the electrodelands disposed on the mounting surface of the mounting board, and theheight of the inner barrier is lower than the height of the bumps afterthe surface acoustic wave element and the mounting board have beenconnected through the bumps.
 26. A surface acoustic wave device asclaimed in claim 23, wherein at least the inner barrier is made of amaterial that is inferior in wettability against the sealing resin tothe functional surface of the surface acoustic wave element and themounting surface of the mounting board.
 27. A surface acoustic wavedevice as claimed in claim 23, wherein the inner barrier includes afirst inner barrier and a second inner barrier.
 28. A surface acousticwave device as claimed in claim 27, wherein the first inner barrier andthe second inner barrier have nearly the same height.
 29. A surfaceacoustic wave device as claimed in claim 27, wherein the first innerbarrier and the second inner barrier are made of the same material. 30.A surface acoustic wave device as claimed in claim 23, wherein the outerbarrier has a level difference.
 31. A surface acoustic wave device asclaimed in claim 22, wherein the level difference in the outer barrieris defined by at least one concave portion.
 32. A surface acoustic wavedevice as claimed in claim 22, wherein the level difference in the outerbarrier is defined by at least one convex portion.
 33. A surfaceacoustic wave device comprising: a surface acoustic wave element having,on a functional surface thereof, a vibrating portion including at leastone comb-shaped electrode portion disposed on a piezoelectric substrate;a mounting board; and a sealing resin; wherein the surface acoustic waveelement and the mounting board are connected through bumps so that themounting surface of the mounting board and the functional surface of thesurface acoustic wave element face each other, an outer peripheral edgeof the surface acoustic wave element is sealed by the sealing resin, anda vibration space is secured between the vibrating portion of thesurface acoustic wave element and the mounting surface of the mountingboard; and a first outer barrier disposed so as to enclose the bumps andthe vibrating portion and a second outer barrier disposed inside thefirst outer barrier so as to enclose the bumps and the vibrating portionare provided on the functional surface of the surface acoustic waveelement.
 34. A surface acoustic wave device as claimed in claim 33,wherein the first outer barrier is higher than the second outer barrier.35. A surface acoustic wave device as claimed in claim 34, wherein theheight of the first outer barrier is lower than the total height of thebumps after the surface acoustic wave element and the mounting boardhave been connected through the bumps and the electrode lands disposedon the mounting surface of the mounting board, and the height of thesecond outer barrier is higher than the height of the bumps after thesurface acoustic wave element and the mounting board have been connectedthrough the bumps.
 36. A surface acoustic wave device as claimed inclaim 33, wherein the first outer barrier includes at least two layers,and the lowest layer of the first outer barrier has the same height asthe second outer barrier.
 37. A surface acoustic wave device as claimedin claim 33, wherein at least the second outer barrier is made of amaterial that is inferior in wettability against the sealing resin tothe functional surface of the surface acoustic wave element and themounting surface of the mounting board.
 38. A surface acoustic wavedevice as claimed in claim 37, wherein the first outer barrier containsa level difference.
 39. A surface acoustic wave device as claimed inclaim 38, wherein the level difference in the first outer barrier isdefined by at least one concave portion.
 40. A surface acoustic wavedevice as claimed in claim 38, wherein the level difference in the firstouter barrier is defined by at least one convex portion.
 41. A surfaceacoustic wave device as claimed in claim 22, wherein a board-sidebarrier is disposed on the mounting board so as to face the outerbarrier.
 42. A surface acoustic wave device as claimed in claim 41,wherein the total height of the outer barrier and the board-side barrieris lower than the total height of the bumps after the surface acousticwave element and the mounting board have been connected through thebumps and the electrode lands disposed on the mounting surface of themounting board.